1. Field of the Invention
The present invention relates to orthopedic prosthetic devices and particularly to an improved spinal cage prosthesis. Even more particularly the present invention relates to an expandable generally cylindrically shaped spinal cage prothesis that includes upper and lower components that can be incrementally separated from one another by an advancing screw until they are in contact with the vertebral plates of the involved spinal unit for use in vertebral fusion procedures. The present invention also relates to a surgical method for installing the spinal cage prothesis.
2. General Background
Surgical prosthetic implants have been developed for use in a surgical fusion of the vertebral column. These implants have been provided are in the form of a plug that is placed between two adjacent vertebrae. The plug contacts adjacent vertebral plates to achieve vertebral fusion, thus treating or preventing back pain in patients that have discogenic pain. Many spinal implants in the form of a cage or plug have been patented. An example of a patent for a surgical prosthetic implant that is used in vertebral interbody fusion is the Brantigan U.S. Pat. No. 4,743,256. The '256 patent discloses a surgical prosthetic implant for the vertebral column in the form of a rigid, preferably inert metal plug having a porous metal surface allowing ingrowth of bone cells for biologic fixation is provided to achieve vertebral interbody fusion for treating or preventing back pain. The plug forms a strut spanning and maintaining the disc space between adjoining vertebrae and has opposite ends bottomed in channels that are cut into the opposing faces of the vertebrae or opposed faces bottomed on the end faces of adjoining vertebrae. Bone ingrowth into the porous surface of the plug achieves long term biological fixation with living bone. Local bone graft harvested from the channel cuts into the vertebrae to receive the plug supplements the fusion. The implant minimizes or eliminates the need for bone graft material obtained from a second surgical site or from a bone bank and simplifies the method of achieving the interbody fusion.
In the Shepperd U.S. Pat. No. 4,863,476, there is disclosed a spinal implant that has an elongated body which is divided into two portions with mutually opposed contact surfaces and is for insertion into the Joint space between two adjacent vertebrae. A cam device or cam devices are movable between the contact surfaces to expand or increase the spacing between the body portions so as to increase the spacing between the adjacent vertebrae.
The Brantigan U.S. Pat. No. 4,878,915 entitled "Surgical Prosthetic Implant Facilitating Vertebral Interbody Fusion" discloses a prosthesis plug forming transverse struts between adjacent vertebrae.
The Michelson U.S. Pat. No. 5,015,247 entitled "Threaded Spinal Implant" discloses an artificial implant which when placed between two adjacent vertebrae directly participates and is incorporated in the ensuing fusion.
The Ray U.S. Pat. No. 5,026,373 discloses a fusion cage having an external thread that can be surgically inserted into threaded bore extending laterally between the adjacent bony structures such as two vertebrae with the thread penetrating into cancellous bone of each of the vertebrae. The cage is easily screwed into place by hand without damage to bony structures. The cage is then packed with a bone-growth-inducing substances such as cancellous bone.
A middle expandable intervertebral disc implant is the subject of U.S. Pat. No. 5,171,278. The '278 patent discloses an artificial disc implant having a member for adapting in size and shape to an anatomical space between vertebrae and apparatus for expanding the member to conform to the space.
A Canadian Patent Application 2,015,507 discloses a spinal implant for use in surgical procedures for stabilizing the spine.